This application claims the priority of Japanese patent application Serial No. P11-288802 filed on Oct. 8, 1999.
1. Field of the Invention
The present invention relates to a high photo-sensitivity curable resin that can be hardened(cured) by a little exposure amount, a high photo-sensitivity curable resin composition containing such a photo-curable resin, and a production method thereof.
The present invention also relates to a high photo-sensitivity curable resin having a high as well as a high sensitivity, which has no risk of bringing about undesired increase of the molecular weight or the viscosity in storage, use, or handling, such as a photo-curing resin with a good storage property, and a production method thereof.
The present invention also relates to a photo-curable resin composition containing the photo-curable resin with the high sensitivity and high stability, capable of easily adjusting or evening the film thickness of a coated film without the risk of viscosity increase in storage or coating, and a production method thereof.
Moreover, the present invention relates to a high sensitivity and transparent photo-curable resin, a high sensitivity and transparent photo-curable resin composition containing such a photo-curable resin, and their production methods.
Still further, the present invention relates to a color filter and a liquid crystal display panel with little color irregularity and contrast irregularity, with a protection film of a color layer and a spacer of a liquid crystal layer formed by using the photo-curable resin composition mentioned above.
2. Description of the Related Art
Recently, as a flat display for a personal computer, color liquid crystal display devices have been propagated rapidly. As shown in FIG. 1, a color liquid crystal display device 101, in general, has a structure wherein a color filter 1 and an electrode substrate 2 such as a TFT substrate are faced with each other so as to provide a gap part 3 of about 1 to 10 xcexcm, with a liquid crystal compound L filled in the gap part 3 and the periphery thereof sealed by a sealing member 4. The color filter 1 comprises a structure including a black matrix layer 6 formed in a predetermined pattern for blocking the light in the boundary part between the pixels, a color layer 7 with a plurality of colors (in general, three primary colors including red (R), green (G), and blue (B)) arranged in a predetermined order for forming each pixel or recently, a color filter, a protection film 8, and a transparent electrode film 9 successively laminated on a transparent substrate 5 in this order from the side close to the transparent substrate. Moreover, an alignment layer 10 is provided on the inner surface side of the color filter 1 and the electrode substrate 2 facing thereto. Furthermore, pearls 11 having a constant particle size are dispersed as a spacer in the gap part 3 for constantly and homogeneously maintaining the cell gap between the color filter 1 and the electrode substrate 2. A color image can be obtained by controlling the light transmittance of the pixels colored in each color or the liquid crystal layer behind the color filter.
The protection film 8 formed in the color filter serves for protecting the color layer and for flattening the color filter in the case a color layer is provided in the color filter. In a color liquid crystal display device, in the case the flatness of the transparent electrode film 9 is deteriorated due to existence of gag irregularity derived from the waviness on the surface of the transparent substrate of the color filter, gap irregularity among the R, G and B pixels, or gap irregularity within each pixel, color irregularity or contrast irregularity is generated so as to give rise to a problem of the image quality deterioration. Therefore, a high flatness is required to the protection film.
In the case the fine particle-like pearls 11 as shown in FIG. 1 are dispersed as the spacer, the pearls are dispersed randomly, independent from being behind the black matrix layer 6 or behind the pixels. In the case the pearls are disposed in the display area, that is, in the pixel part, a back lighting beam transmits the pearl part, and further, the orientation of the liquid crystal is disturbed in the vicinity of the pearls so that the display image grade is deteriorated remarkably. Then, as shown in FIG. 2, instead of dispersing the pearls, column-shaped spacers 12 having a height corresponding to the cell gap are formed on the inner surface side of the color filter in the area coinciding with the black matrix layer 6.
The above-mentioned protection film 8 and the column-shaped spacers 12 can be formed with a resin. In consideration of the adhesion property and the sealing property of the sealing part, the protection film 8 is preferably one capable of covering only the area of the transparent substrate with the color layer formed thereon. Moreover, the column-shaped spacers 12 need to be formed accurately in the area with the black matrix layer formed, that is, in the non-display area. Therefore, the protection film and the column-shaped spacers came to be formed with a photo-curing resin capable of easily limiting the area to be hardened by a photo mask.
Furthermore, in the case the surface applied with a photo-curing resin is developed with an organic solvent after exposure for forming the protection film or the column-shaped spacers, since handling and the waste liquid process are troublesome so that it is not satisfactory in terms of economy and stability, a photo-curing resin allowing an alkaline development after exposure has been developed by introducing an acid functional group in a photo-curing resin.
As an alkaline-soluble photo-curing resin, for example, o-cresol novolak epoxy acrylate, or the like, having about 2,000 weight average molecular weight is known. The resin has a carboxylic acid group defining the alkaline solubility. However, since the resin uses a monomer component as an acryloyl group defining the curing property, the reliability in film formation is low. For example, it involves the risk of the residual monomer unit elution to the liquid crystal part. Furthermore, the film thickness may be reduced due to a large amount of the elution in the alkaline development.
Moreover, as all method for introducing a radical polymerizable group such as an acryloyl group into the molecular structure of a compound or providing the photo curing property, for example, a method Of introducing a radical polymerizable group such as a methacryloyl group to an end by reacting of diols with excessive diisocyanate for preparing a reaction product with an isocyanate group remaining on the end, and reacting the isocyanate group of the reaction product with 2-hydroxyl ethylmethacrylate for producing urethane acrylate, is known. However, according to the method, as a principle, a (meth)acryloyl group can be introduced to only both ends of the molecular structure. Furthermore, although a method of radical polymerization by partially containing a compound having two or more radical polymerizable groups in a molecular such as a (meth)acryloyl group can be conceivable, the content of the radical polymerizable group cannot be controlled as well as a problem of gellation is also involved.
As mentioned above, although it is convenient to form the protection film and the column-shaped spacers of a color film with a photo-curing resin, it is difficult to control the amount of the alkaline soluble group such as a carboxyl group and the radical polymerizable group such as a (meth)acryloyl group according to the conventional photo-curing resin in consideration of the curing property and the alkaline solubility thereof.
According to the undisclosed knowledge obtained by the study of the present inventor, since the amount of the alkaline soluble carboxyl group and the radical polymerizable (meth)acryloyl group can be adjusted freely according to a copolymer resin having a principal chain comprising at least a component unit represented by the below-mentioned formula (1) and a component unit represented by the below-mentioned formula (2), with at least a part of the carboxyl group or the hydroxyl group thereof bonded with a (meth)acryloyloxy alkyl isocyanate compound represented by the below-mentioned formula (5) according to reaction of the isocyanate group of the compound, it is extremely suited as a photo-curing resin: 
wherein R is hydrogen or an alkyl group having 1 to 5 carbon atoms, R1 is an alkylene group having 2 to 4 carbon atoms, R4 is an alkylene group, and R5 is hydrogen or methyl.
However, it is learned that in the case the above-mentioned copolymer resin is dissolved or dispersed in a solvent and left, the molecular amount is increased rapidly so as to raise the viscosity According to our experiment, it is confirmed that the thickening phenomenon proceeds even in a room temperature, and proceeds more rapidly as the storage temperature is higher. Moreover, in an experiment utilizing the GPC (gel permeation chromatography), only by dissolving the above-mentioned copolymer resin in a solvent and leaving the same in a room temperature for two weeks, the molecular weight, which was 69,000 at the time of preparation, was increased to as much as 98,000, and the viscosity of the solution became 1.17 times. Furthermore, by storing the copolymer resin at 70xc2x0 C. for three days, the molecular weight, which was 69,000 at the time of preparation, was increased to as much as 340,000, and the viscosity of the solution became 2.14 times. Moreover, it is also confirmed that the thickening phenomenon becomes further remarkable by mixing the copolymer resin with a thermosetting epoxy resin, an acrylic monomer, a polymerization initiator, or the like, dissolving in a solvent, and storing in the state of a coating liquid to be actually used. Since the above-mentioned copolymer resin cause such a phenomenons of increasing in viscosity, it is the lack of shelf life and is apt to cause coating unevenness.
In particular, the extremely high accuracy and homogeneity are required for the film thickness of the color layer, the protection film for covering the color layer or the height of the column-shaped spacers for ensuring the cell gap. Compared with the color layer and the protection film which is to be formed continuously in a collective area on one side of the substrate, since the column-shaped spacers are formed intermittently according to the black matrix layer formation area by a height more than double as much as the height of the color layer, the size fluctuation can easily be brought about due to increase of the viscosity of the coating liquid. Moreover, in the case the coating resin came to have too high a molecular amount, the shape of the column-shaped spacers is deteriorated so that the strength as a spacer and other dynamic characteristics are deteriorated as well.
Therefore, in the case of forming the color layer, the protection film or the column-shaped spacer of a color filter, in particular, of forming the column-shaped spacer, using a coating liquid of a photo-curing resin composition containing the above-mentioned copolymer resin, the thickening phenomenon of the coating liquid should be prohibited to a minimum level.
Furthermore, a good transparency is required to a resin for forming the color layer or the protection layer of a color filter. However, according to the knowledge of the present inventors, the above-mentioned copolymer resin does not have a sufficient transparency.
In view of the circumstances, the present invention has been achieved, and a first object thereof is to provide a method of improving the sensitivity of the above-mentioned photo-curable copolymer resin and to provide a photo-curable resin having higher sensitivity than any one obtained conventionally.
A second object of the present invention is to provide a method of improving the shelf life and stability, as well as the sensitivity of the above-mentioned photo-curable copolymer resin and to provide a photo-curable resin which has higher sensitivity than any one obtained conventionally and which is hard to increase in viscosity.
A third object of the present invention is to provide a method of improving the transparency as well as the sensitivity, of the above-mentioned photo-curable copolymer resin, and to provide a photo-curable resin which has higher sensitivity than any one obtained conventionally and which is excellent in transparency.
A forth object of the present invention is to provide a high sensitive photo-curable resin composition containing the above-mentioned improved photo-curable resin.
A fifth object of the present invention is to provide a color filter and a liquid crystal display panel in which a color layer, a protection film and/or a column-shaped spacer in a cell gap are formed by using the above-mentioned improved photo-curable resin composition.
The high photo-sensitivity curable resin to be provided in the present invention comprises a polymer having a principal chain which comprises a constitutional unit having an acid functional group and a constitutional unit having a hydroxyl group, wherein an isocyanate compound containing a radical polymerizable group is amide-bonded with at least a part of said acid functional group via an isocyanate group of the isocyanate compound and/or urethane-bonded with at least a part of said hydroxyl group via the isocyanate group of the isocyanate compound, and the feed amount of said isocyanate compound containing the radical polymerizable group is 1.0 or more in terms of the equivalent ratio of said isocyanate group to said hydroxyl group in the principal chain (NCO/OH).
Side chains of the radical polymerizable groups can be introduced into the photo-curable resin at a high rate by controlling the feed amount of an isocyanate compound containing the radical polymerizable group so that the equivalent ratio (NCO/OH) is 1.0 or more. As a result, the sensitivity of the photo-curable resin can be improved. Further, in the high photo-sensitivity curable resin of the present invention, because the content of a constitutional unit having an acid functional group can be controlled at a proper rate, the alkali-solubility (developing property) can be controlled freely.
The content rate of the constitutional unit having the hydroxyl group is preferable to be kept at 14 mol % or more in the feed amount, as well as controlling the above-mentioned equivalent ratio of the isocyanate group (NCO/OH) to be 1.0 or more. Because the introduction rate of the isocyanate group is raised by controlling the above-mentioned equivalent ratio of the isocyanate group (NCO/OH) to be 1.0 or more, and at the same time, the reacting part of the isocyanate group is increased by making the feed amount of the constitutional unit having the hydroxyl group to be 14 mol % or more, it becomes possible to introduce the side chains of the radical polymerizable group into the photo-curable polymer in very large quantities, resulting in the gain of especially high sensitivity.
The upper limit of the feed amount of the isocyanate compound containing radical polymerizable groups is preferable to be controlled so that the above-mentioned equivalent ratio of the isocyanate groups (NCO/OH) is 2.0 or less. When the above-mentioned equivalent ratio (NCO/OH) is more than 2.0, a lot of unreacted isocyanate compounds are remained in the obtained photo-curable resin, resulting in lowering physical properties of the photo-curable resin.
Normally, unreacted isocyanate compounds remain in the photo-curable resin of the present invention. The amount of the isocyanate compound containing the radical polymerizable group which is actually introduced as side chains into a photo-curable polymer, an essential component of the photo-curable resin, can be measured with 1H-NMR. After removing components of 5000 or less in weight-average molecular weight in terms of polystyrene from the photo-curable resin of the present invention by a method of reprecipitation refining and the like, when an amount of the double bonds of the isocyanate compound containing the radical polymerizable group which is introduced into a high molecular weight fractionation of a photo-curable polymer is measured with 1H-NMR, the amount of the residue of the isocyanate compound containing the radical polymerable group to 100 mol of constitutional units of the principal chain reaches to 8 mol or more.
The production method of the high photo-sensitivity curable resin in the present invention is characterized by reacting an isocyanate compound containing the radical polymerizable group with a raw material polymer having a principal chain comprising at least a constitutional unit having an acid functional group and a constitutional unit having a hydroxyl group at the rate of 1.0 or more in terms of the equivalent ratio of the isocyanate group to the hydroxyl group in the principal chain (NCO/OH).
In one aspect of said production method, the isocyanate compound containing the radical polymerizable group is dropped into a solution made by dissolving or dispersing the raw material polymer in a solvent and is reacted. When an isocyanate compound containing the radical polymerizable group is dropped little by little into a solution of the raw material polymer (namely a dropping method), a high photo-sensitivity curable resin is easily obtained even in a condition that the feed amount of an isocyanate compound is relatively small that is, the equivalent ratio of the isocyanate group to the hydroxyl groups (NCO/OH) is near 1.0.
In the present invention, after a high photo-sensitivity curable resin is synthesized by reacting the isocyanate compound containing the radical polymerizable group with a raw material polymer having a principal chain comprising at least a constitutional unit having an acid functional group and a constitutional unit having a hydroxyl group, the stability of the high photo-sensitivity curable resin can be improved by reacting it further with an alcohol. It is presumed that the high photo-sensitivity curable resin treated with an alcohol has a molecular structure in which alcohols are bonded to at least part of acid functional groups in the principal chain of the high sensitivity resin via the hydroxyl groups of the alcohol. When a high sensitivity resin is treated with alcohol, since increase in viscosity becomes hard to be caused, the shelf life is improved, in addition, since it becomes easy to control coating, coating unevenness is hardly caused.
In the present invention, when the raw material polymer for a photo-curable resin, that is, the principal chain part of the photo-curable polymer is formed, it is preferable to carry out the polymerization reaction by using an azo polymerization initiator of non-nitryle series or a polymerization initiator of peroxide series as a polymerization initiator. Moreover, when the isocyanate compound containing the radical polymerizable group is reacted with the raw material a polymer, it is preferable to use a compound selected from the group of compounds of phenol series shown in the following formula (9) and compounds of phosphite series shown in the following formula (15) as a polymerization inhibitor. In cases where the high photo-sensitivity curable resin is formed by using the above-mentioned specific polymerization initiator and/or the above-mentioned specific polymerization inhibitor, the obtained liquid after the reaction shows a high light transmittance in the range of visible and ultraviolet light. Consequently, even if the reaction liquid containing the high photo-sensitivity curable resin is used without purifying as a coating liquid as it is, it is possible to form a film excellent in transparency because the liquid has a small quantity of coloring components. Further, the film is also excellent in exposure sensitivity because the reaction liquid has a high light transmittance in the range of ultraviolet light: 
wherein R6 is hydrogen, an alkyl group having 1 to 5 carbon atoms, or the following formula (10): 
wherein D is xe2x80x94Sxe2x80x94, an alkylene group having 1 to 10 carbon atoms or an alkylidene group having 1 to 10 carbon atoms. R7 is hydrogen or an alkyl group having 1 to 10 carbon atoms. R8 is hydrogen, an alkyl group having 1 to 10 carbon atoms or the following formula (11): 
Here, R10 in the formula (11) is an alkylene group having 1 to 10 carbon atoms or an alkylidene group having 1 to 10 carbon atoms, R9 is hydrogen or an alkyl group having 1 to 10 carbon atoms. However, at least one of R7 and R8 is a tertiary butyl group or an alkyl group having a cyclohexyl group. And substituents indicated with the same code may be the same one or different each other. 
wherein R11 is hydrogen or an alkyl group having 1 to 20 carbon atoms.
By using the above-mentioned specific polymerization initiator and/or the above-mentioned specific polymerization inhibitor, an improved light transmittance can be provided. For example, when a solution of the high photo-sensitivity curable resin in a 3-methoxybutyl acetate of 20 wt. % as resinous solid content is prepared by diluting the reaction liquid containing the high photo-sensitivity curable resin as it is with 3-methoxybutyl acetate, or dissolving the high photo-sensitivity curable resin isolated from the reaction liquid in 3-methoxybutyl acetate, and then this prepared solution is put into a quartz cell of 1 cm square, the light transmittance shows 60% or more at 400 nm in the range of visible light or 50% or more at 360 nm in the range of ultraviolet light.
The photo-curable resin composition to be provided in the present invention is characterized by containing the above-mentioned high photo-sensitivity curable resin as an essential component. The photo-curable resin composition of the present invention succeeds wholly the excellent properties of the high photo-sensitivity curable resin as an essential component. That is, the productivity of film formation is high because the composition can be hardened in a short time at a small exposure amount. Furthermore, since increase in viscosity becomes hard to be caused by treating the high photo-sensitivity curable resin with alcohol, the composition are excellent in shelf life and coating controlability. As a result, coating films with uniform thickness and patterns with accurate size and shape can be obtained. In addition, the composition is also excellent in transparency, and it is possible to form a film which is required transparency.
According to the present invention, it is possible to obtain a photo-curable resin composition having an excellent sensitivity.
That is, a minimum exposure amount of said photo-curable resin composition can be made to be 100 mJ/cm2 or less when said photo-curable resin composition is applied on a base plate and pre-baked to form a coated film, the coated film is exposed and the film thickness is measured (the film thickness before development), then the exposed coated film is developed and the film thickness is measured again after post-baking (the final film thickness after hardening), and the residual film rate is measured according to the following equation,
Residual film rate (%)=(final film thickness after hardening (xcexcm)÷film thickness before development (xcexcm))xc3x97100,
on the other hand, the same photo-curable resin composition is applied on a base plate in the same conditions as those for measuring the residual film rate, the film thickness is measured after the coated film is pre-baked and completely hardened by exposing (the completely exposed film thickness), then the exposed coated film is post-baked with no developing process in the same conditions as those for measuring the residual film rate, and the film thickness is measured again (the final film thickness without the developing process), and the reference residual film rate is measured according to the following equation,
Reference residual film rate (%)=(final film thickness without the developing process (xcexcm)÷completely exposed film thickness (xcexcm))xc3x97100,
thus minimum exposure amount is defined as the smallest exposure amount making he calculated residual film rate equal to the reference residual film rate, provided that the error limit is 1%.
The photo-curable resin composition of the present invention, which is obtained like this, is suitable to form a color layer of a color filter, a protection film coating the color layer, and column-shaped spacers to maintain a cell gap in a liquid crystal display panel. It is possible to precisely form the color layer and the protection film of desired thickness, and the column-shaped spacers of desired height.